Tone arm for phonographs



Feb. 19, 1963 K. KRBER 3,078,100

TONE: ARM FOR PHONOGRAPHS Filed Aug. 2, 1950 sgfllllrlII/l/J r I-l l Il.jf-l (C gl l() l l T I l w (Q i I I l LJ ,l ...l

INVE TOR ATTO R N EY5 ilnited tates 3,078,100 TGNE ARM FR PHONSGRAPHSKlaus Krller, Gutenbergstrasse 65, Potsdam, Germany Filed Ano. 2, 1960,Ser. No. 47,912 Claims priority, application Germany Feb. 2S, 1960 3tlaims. (Cl. 274-23) The present invention relates to a bearingarrangement `for the tone arm of a record player.

Several kinds of bearing arrangements for tone arms of record playersare known which are all based on two associated bearing elements, eg.,knife edge bearings, slide bearings, or point bearings. The shortcomingsof these bearings are due to the more or less considerable frictionforces which will become active between the bearing elements. In ballbearings these forces are, of course, least felt, but ball bearings willnot function without play; that, however, is a necessity for thevertical movement of the tone arm because of the scanning of the needle.

The microgrooves which are now generally used in long-playing records,require a very light, sensitive scanning by the needle of the pick-updevice. The pendulum movement of the tone arm in vertical as well as inhorizontal direction, which is a consequence of the produc tiontolerances of the records, causes the oil film between bearing elementsto disappear so that a dry friction results. The friction forces arevery much increased thereby and in point bearings an increase of up to2/3 of the original force has been found.

It is known that to save the record and the needle from excessive wear,a certain maximum contact force is admissible, which is determined bythe necessary guidance of the needle in the very line micro groove inorder that it may render all recorded undulation in true form. Anattempt has to be made to keep the minimum Contact force as low aspossible.

The indicated friction forces caused by dry friction in slide bearingslead to the following undesirable occurrences, particularly noticeableat a low pitch:

(l) Due to the friction loss in the bearing the contact force has to beundesirably increased when the tone arm head oscillates up and down inorder to guarantee the guidance of the needle in the microgroove and toavoid slipping of the needle out of the groove when the record movesdown. The increase in the contact force results in undue wear of theneedle and the record. At the same time, during rotation, the contactforce of the needle will vary continually. The varying contact forcesare transmitted to the resilient rubber bearing of the needle whichtherefore is under unequal tension and the needle will scan undulationsunevenly and this, in turn, will lead to tone distortions in theloudspeaker.

(2) Due to the friction forces in the slide bearing the lateral contactpressure of the needle is subject to variations by oscillating movementsoccuring in the scanning of the record spiral, which will likewiseintiuence the loudspeaker and lead to distortions due to uneven lateralscanning by the needle.

It is the object of the present invention to overcome theabove-mentioned disadvantages of the present pick-up devices.

In accordance with the invention, the disadvantages of bearing frictionare overcome for the vertical movement Patented Feb. 19, 1963 of thetone arm by providing a connection for the arm with a supporting portionin the form of a flexible band, for example, a short leaf spring which,due to its particular arrangement, is permanently under tension. Thisflexible connection has no friction except internal molecular friction.The contact force for the needle can thus be considerably reduced, afactor which will not only reduce wear of the records and the needle,but will also result in much improved sound and result in very naturaltone rendition in the loud speaker over the entire frequency range.

The invention will be fully understood from the following descriptionand the accompanying drawings in which:

FIG. 1 is a longitudinal section through the tone arm; and

FIG. 2 is a front view of the flexible connection.

ln the drawing, the tone arm is designated by l. The weight of the armacts against the spreading pressure of a spring 3 which is adjustable bya screw 2. The needle is shown at 4. The resulting contact force of theneedle is, for instance, adjusted to be 6 grams. A leaf spring 5replaces the known bearings for resiliently connecting the tone arm 6with a supporting member 7 and is permanently under tension, as forinstance the pendulum spring in a pendulum clock. Leaf spring 5 isfastened to brackets or tianges 10 and 11 by screws 12 extending throughbacking plates 13 and 14.

A ball bearing 9 is provided for the vertical shaft 8 of the supportingmember 7. The bearing 9 is protected by an enclosure and runs with onlya dry dusting of molybdenum disulfide. At this location, the play of theball bearing does not produce any disadvantage, because it isunilaterally loaded by the total weight of the tone arm.

The invention has been illustrated by one embodiment thereof, but itwill be understood that the invention is not to be construed as limitedexcept as defined in the following claims.

I claim:

1. A tone arm for use in phonographs, having a lower supporting memberadapted to be rotatably supported from the phonograph, an upperelongated member adapted to support a needle, and means connecting saidupper and lower members, said means including first substantiallyvertically disposed spring means and second spring means.

2. A tone arm according to claim l, wherein said second spring means isadjustable for controlling the weight of the contact force of saidneedle on a phonograph record.

3. A tone arm according to claim 1, wherein said first verticallydisposed spring means comprises a leaf spring, the longitudinal axis ofsaid leaf spring being perpendicular to the longitudinal axis of saidtone arm.

References Cited in the tile of this patent UNITED STATES PATENTS2,224,332 Alsbrook Dec. 10, 1940 2,622,993 McCullough Dec. 23, 19522,941,810 Wagner June 21, 1960 FOREIGN PATENTS 722,876 Germany July 23,1942 555,519 Great Britain Aug. 26, 1943

1. A TONE ARM FOR USE IN PHONOGRAPHS, HAVING A LOWER SUPPORTING MEMBERADAPTED TO BE ROTATABLY SUPPORTED FROM THE PHONOGRAPH, AN UPPERELONGATED MEMBER ADAPTED TO SUPPORT A NEEDLE, AND MEANS CONNECTING SAIDUPPER AND LOWER MEMBERS, SAID MEANS INCLUDING FIRST SUBSTANTIALLYVERTICAL DISPOSED SPRING MEANS AND SECOND SPRING MEANS.